1. Field
The present disclosure is directed to a method and apparatus for scheduling uplink transmissions with reduced latency. More particularly, the present disclosure is directed to wireless communication device transmissions using a shortened transmit time interval.
2. Introduction
Presently, In Long Term Evolution (LTE) communication systems, time-frequency resources are divided into subframes where each 1 ms subframe has two 0.5 ms slots and each slot has seven Single Carrier Frequency Division Multiple Access (SC-FDMA) symbols in the time domain for uplink transmissions. In the frequency domain, resources within a slot are divided into Physical Resource Blocks (PRBs), where each resource block spans 12 subcarriers.
In current LTE systems, User Equipment (UE) uplink data is scheduled using a 1 ms minimum Transmission Time Interval (TTI). Within each scheduled TTI, the UE transmits data over a Physical Uplink Shared CHannel (PUSCH) in PRB-pairs indicated by an uplink grant that schedules the data transmission to the UE. Each PRB-pair comprises two PRBs, with one PRB in each slot. For FDD systems, if an uplink grant is received in subframe n, the UE transmits PUSCH in subframe n+4 in response to the grant and looks for an ACK/NACK corresponding to that transmission in subframe n+8. If a NACK is indicated, the UE will retransmit in subframe n+12 resulting in a HARQ round trip delay of 8 ms. TDD systems typically have a similar or longer round trip delay. This causes latency that delays transmission and reception of communication signals.
Thus, there is a need for a method and apparatus for scheduling uplink transmissions with reduced latency.